British patent specification No. 1,085,791, dated 16th April 1964, describes:
"An apparatus for providing a desired atmosphere in a sleeping space, comprising frame members arranged to support, when said apparatus is in use, a cover which co-operates with a bed to define a sleeping space for the body and legs of a person while leaving the head of the person outside the sleeping space, temperature-changing means for heating and/or cooling said space, and supporting means supporting said frame members, the frame members being longitudinally adjustable to adjust the length of said sleeping space, and said supporting means being vertically adjustable to raise and lower said frame members."
Experience proved this apparatus to be impractical because whatever fabric was used for the cover, a very considerable volume of air, usually heated, was required to be blown into the sleeping space by the heating means. This was because of the porosity of the cover. Even heavy canvas was tried, but still problems were experienced. The apparatus was found to have to be too bulky, powerful and expensive to be practical.
Due to continuing incentive for energy saving, we have reconsidered the earlier invention. In the intervening time, many new light-weight materials have been developed. In particular light-weight insulating covers are now available.
The significance of the availability of these is that we have been able not only to introduce routine improvements by using lighter weight structural materials, we have also been able to make innovative changes in the earlier apparatus.
In particular, we have now been able to enclose the space between the cover and the mattress. This has resulted in the ability to recirculate air flow from and back to this space.